Information reproduction utilizing electret material

ABSTRACT

A master for electrostatic reproduction is provided in which information to be duplicated is defined by electret material raised in relief from the surface of a support sheet. The master is obtained by thermal or impact transfer of electret or electret-forming material from a transfer sheet. In one general form of the invention, the material is thermally transferred and cooled under a polarizing D-C potential gradient. In other forms of the invention, material is transferred to the master either as electret-forming material, whereupon it is subsequently polarized, or as pre-formed electret material.

United States Patent 1 1 Gaynor 1 1 INFORMATION REPRODUCTION UTILIZING ELECTRET MATERIAL [75] Inventor: Joseph Gaynor, Arcadia. Calif.

[73] Assignee: Bell & Howell Co., Pasadena, Calif.

[22] Filed: June 21, 1973 [21] Appl. No.: 372,373

Related US. Application Data [63] Continuation of Ser. No. 110,491, Jan. 28, 1971,

abandoned.

[52] US. Cl l0I/467; 96/1 E; 101/DIG. 13; 117/364 [51] Int. Cl B4Im 5/18; 841m 5/20 [58] Field 01' Search 96/1 R, 1 E, 1.3; [01/471, l0l/DIG. 13; 117/361, 36.3, 36.4

[56] References Cited UNITED STATES PATENTS 2,808,777 113/1957 Roshkind 101/471 X 3.000.735 9/1961 Gunning I 96/].5 3,005,707 10/1961 Kallmann et a1... 96/15 3,122,998 3/1964 Raczynski et a1... 101/471 3,199,086 8/1965 Kallmann et a1.... 96/].5 X 3,205,301 9/1965 Etcheverry 178/66 A June 10, 1975 3,268,331 8/1966 Harper 96/1 R 3,364,020 1/1968 Fehlberg et a1. 96/1 R 3,379,127 4/1968 Newman 101/471 3,406,060 10/1968 Schlein et a1. 96/1 3,548,748 12/1970 Van Dorn 101/471 3,552,317 1/1971 Ritzerfeld 101/471 Primary Examiner-Clyde I. Coughenour Attorney, Agent, or Firm-Nilsson, Robbins, Bissell, Dalgarn & Berliner 5 7 ABSTRACT 4 Claims, 10 Drawing Figures INFORMATION REPRODUCTION UTILIZING ELECTRET MATERIAL This application is a continuation of Ser. No. l l0,491, filed Jan. 28, 1971, now abandoned.

FIELD OF THE INVENTION The fields of art to which the invention pertains include the fields of electrostatic recording, electret formation and planographic processes.

BACKGROUND AND SUMMARY OF THE INVENTION Electret materials have been utilized in a variety of re oduction techniques. For example, U.S. Pat. No. 3, 64,020 to Fehlberg et al. discloses that an electret layer can be formed with an electrostatic image by irradiation in the presence of a D-C potential or by irradiation subsequent to blanket electret formation. Thereafter the image can be developed with toner and electrostatically transferred to a copy sheet. U.S. Pat. No. 3,276,031 to Gaynor. U.S. Pat. No. 3,214,272 to Ploke and U.S. Pat. No. 3,318,698 to Schwertz disclose processes in which photoconductive electrets are imagewise discharged and the charged portions are then heat deformed. U.S. Pat. No. 3,000,735 to Gunning et al. utilizes an electret plate to induce a charge on a conventional photoconductive plate, replacing corona discharge apparatus. U.S. Pat. No. 2,986,524 to Padgett discloses the use of waxy material as an electret. Other patents broadly of interest with respect to the present invention include U.S. Pat. Nos. 1,997,263, 2,046,476, 2,740,184, 3,005,707, 3,199,086, 3,205,30l 3,406,060, 3,477,846 and 3,496,013. The prior art has used electret materials as a means for forming a latent image which is subsequently developed by the application of toner, the toned image being electrostatically transferred to copy paper. The latent image is defined by electret material against a background of chemically and physically identical, but non-electret, material. Because of surface and mechanical effects, when such images are toned, particularly with liquid toner, pigment tends to adhere to background areas, resulting in poor quality copies.

A variety of other duplicating processes are well known which are of interest to the present invention. Among such processes are those involving impact and thermal transfer techniques. for example, soluble dye transfer or spirit duplicating processes. Such processes involve the transfer of dye bearing material from a transfer sheet to a receiving, master sheet. The master sheet is placed on a rotating drum and contacted with a succession of sheets of copy paper previously wet with a volatile alcohol solvent. The solvent dissolves part of the dye in the master image and transfers it to the copy paper and this process is continued until the dye is effectively exhausted.

Several techniques are available to transfer dyebearing material from the transfer sheet to the master sheet. With one technique, information is typed onto the rear of the transfer sheet which is sandwiched with the master sheet and dye-bearing material is impact transferred. With another technique, the information to be recorded is thermally transferred by pressing an original document to be duplicated in contact with the transfer sheet and master sheet and exposing the assembly to infrared radiation. The transfer material is softened in areas corresponding to the image areas on the original document and the softened material is transferred to the master sheet. For a detailed discus sion of various duplicating piQcesses utilizing such materials, reference can be made to U.S. Pat. Nos. 3,122,997 and 3,122,998 to Raczyinski. A drawback of such processes is the limitation in type and density of image color. Furthermore, the number of copies 0btainable with such processes is limited to the quantity of dye transferable from the dye-bearing material by solvent leaching.

The present invention provides a duplicating process which incorporates features of each of the foregoing processes but which overcomes to a large extent the aforenoted drawbacks. In the present invention, an assembly of transfer sheet and master sheet is provided which can be chemically and physically similar to the sandwiched assembly utilized in spirit duplicating processes, but in place of dye-impregnated transfer material there is utilized electret or electret-forming material. The transfer sheet has a surface coated with electret or electret-forming material and an electrically conductive master sheet is disposed with its receiving surface in contact with the transfer material. This material is selectively transferred to the master sheet either as electret material or under conditions resulting in a conversion of the transfer material to electret material. A design is thus formed on the master sheet, in representation of the information to be duplicated, in the form of electret material raised in relief from the receiving surface of the master sheet. Toner applied to the master sheet adheres to the design portions as a result of the electrostatic attraction of the electret material and is electrostatically transferred to a copy sheet, without destroying the electret properties of the raised material. The master sheet can be retoned to provide another copy, the process being repeatable any desired number of times as physically feasible.

It will be appreciated that a simple method is provided enabling reproduction in black color or any color available with state of the art toner powder and solutions. The master and transfer material are clean and do not contaminate contacting objects with soluble dye. No solvent is required, thereby eliminating toxicity and'flammability problems, and one is not restricted to spirit soluble compounds for image color and density. Pigments and/or dyes are usable which provide a much wider range of image density and color. Of course, toner transfer need not be limited to electrostatic methods. Toner can be transferred by solvent transfer techniques, or by contact with a tacky substrate on the copy sheet, or thermally by using toner having a melting point lower than the melting point of the wax image.

In one form of the invention the master image is formed by thermal transfer. A D-C potential field is imposed upon the sandwiched assembly of master sheet, transfer sheet and original document and the assembly is exposed to infrared radiation. As a result of selective absorption of the infrared radiation, the electret material is heated and melted selectively in those areas corresponding to the information pattern on the original document. The assembly is then cooled under the D-C potential field which results in the formation of electret in the melted and cooled areas. When the master sheet is separated from the assembly, it will carry away the transfer material in the form of electret which can then be utilized for electrostatic duplication as above described. In a modification of this embodiment, the

.ransfer material is preformed as electret so that either the receiving sheet or the transfer sheet can be utilized as a master sheet for subsequent duplication.

in another embodiment of the invention. the transfer material is impact transferred to the receiving sheet by typing. or the like. and is either preformed as clcctret or is subsequently heated under a polarizing field to electret form.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic. perspective view of a master sheet-transfer sheet-original document assembly in accordance with an embodiment of the present invention;

FIG. 2a is a schematic representation in cross-section of the assembly of FIG. 1 during infrared exposure;

FlG. 2b is a schematic representation of the assembly of FIG 2a following image transfer,

FIG. 3 is a schematic representation of electrostatic printing utilizing a master obtained in accordance with this invention;

FIGS. 4:: and 4b are schematic representations in cross-section of thermal imaging and transfer in accordance with another embodiment of this invention;

FIG. 5 is a schematic representation of a transfer sheet and master sheet following impact transfer; and

H65. 6a. 6b and 6t are schematic representations of successive steps in the impact transfer of non-electret material and subsequent polarization thereof to pro duce a master sheet.

DETAILED DESCRIPTlON invention which may take many forms radically different from the specific illustrative embodiments disclosed. Therefore, specific structural and functional details are not to be interpreted as limiting. but only as a basis for the claims which define the scope of the invention.

Referring to FIG. 1. a sandwich assembly 10 is il lustrated which includes a base sheet 12 of relatively thick paper and which supports an original document 14 to be duplicated. a transfer sheet 16 and an image-- receiving, master sheet 18. The original document 14 contains infrared-absorptive indicia 20 on its face and is placed face-up on the base sheet 12 beneath the relatively thin transfer sheet 16. The transfer sheet 16 is electrically conductive. as described hereinafter in more detail. and carries a thin layer of heat-sensitive electret-forming material 24 on the side opposite the original document 14. The master sheet 18 is also electrically conductive and is disposed with its imagereceiving surface adjacent the heat-sensitive layer 24. The top edges of the transfer sheet 16 and master sheet 18 are secured by adhesive or the like to the top edge 28 of the base sheet 12 so as to provide an easily manip ulated assembly.

Referring additionally to FIGS. 2a and 2b. there is shown a more detailed view of the disposition of the components of the assembly during processing to transfer heat-sensitive material to the master sheet 18. The original document 14 is placed on the supporting base sheet 12 with its infrared-absorptive indicia 20 facing upwardly. The indicia 20 are constituted of carbon. heavy metal. or any material which upon exposure will absorb more infrared radiation than the surrounding non-image areas. so as to convert the absorbed infrared energy to a thermal pattern corresponding to the visible image pattern on the document 14.

The transfer sheet 16 is formed of a substrate 22 which is sufficiently thin. about 0.5 mil, to avoid significant attenuation of the conducted heat pattern. The substrate 22 should have sufficient thermal durability so as to retain mechanical strength at the softening temperature of the electret-forming material 24. Mylar can be used (a transparent. tensilized polyethylene glycol terephthalate polyester film). The transfer sheet substrate 22 is coated with a thin layer 30 of transparent, electrically conductive material so that the transfer sheet 16 is electrically conductive. The electretforming material 24 is coated over the electrically conductive layer 30. The image-receiving master sheet 18 is constructed of a thermally durable substrate 32, eg. of Mylar, coated with a thin layer 34 of infrared transparent electrically conductive material. Since the master sheet must be sufficiently strong to withstand multiple use during subsequent duplication. it is made relatively thick. about l-Z mils.

The assembly of base sheet 12, document 14. transfer sheet 16 and master sheet 18 is sandwiched together under pressure so that directly opposing surfaces are contiguous with one another. Additionally. as indicated schematically in the drawing. electrodes 36 and 38 are placed on the electrically conductive transfer and receiving sheet layers 30 and 34, respectively. and connected via lines 40 and 42 to a source 44 of D-C electrical potential so that a potential gradient is imposed across the transfer material 24. While under the D-C potential. the assembly It) is exposed to radiation 46 rich in infrared rays. directed onto the master sheet 18 so as to penetrate the master sheet 18 and transfer sheet 16 and impinge onto the original document 14. The radiation 46 generates a temperature rise in the indicia 20 portions of the document 14. resulting in a thermal pattern emanating from the document 14 which selectively fuses the transfer material 24 to a softened condition in regions 48 corresponding to the indicia 20. As a result of the imposed D-C field, the fused. softened transfer material 48 is polarized so that upon cooling under the D--(. field. the image pattern is permanently defined by electrct material.

Referring particularly to FIG. 2b, the fused transfer material 48 is transferred to the master sheet 18 so that upon cooling and separating the master sheet 18 from the transfer sheet 16, those portions of transfer material 24 which have been polarized and converted to electret form are carried by the master sheet 18 away from the transfer sheet 16. The result is a master sheet 18 carrying the information to be duplicated in the form of a design of electret material 48 raised in relief from the surface of the master sheet 18. The electret material is formed with equal but opposite charges 50 and 52 on opposite sides of the clcctret layer in accordance with the polarity of the D-C source 44.

A plurality of copies can be prepared from the master sheet 18 without destruction of the electret charges. Referring to FIG. 3, a suitable procedure is depicted wherein the components and materials are schemati cally illustrated. The master sheet 18 is placed on the outer surface of a rotating drum 54 which is provided with a wiping contact arm 56 connected to ground 58. The drum 54 rotates. as indicated by the arrow 60 so as to carry the elcctret material 48 into contact with liquid toner 62 applied from a roller applicator 64. A sheet of copy paper 66 is positioned around a transfer drum 68 which includes a wiping contact arm 70 connected through a resistance 72 to ground 58 and, via a switch 74, to a source 76 of DC potential. In this arrangement, the drums 54 and 68, when charged by closing the switch 74, function as the plates of a capacitor, while the assembly of the electret material 48 and copy sheet 66 functions as dielectric. In response to the application of a potential between the opposing surfaces of the drums 54 and 68, the toner is transferred from the electret material 48 to the copy sheet 66 to define a toner image pattern 78 in correspondence with the pattern of electret material 48. When the copy sheet 66 is rotated from the transfer drum 68, the toner 78 is retained on the copy sheet 66, while the electret material 48 still retains its distributed charges in sufficient intensity to enable redevelopment by reapplication of toner 62. It will be appreciated that in areas of the master sheet 18 such as at 80 where there is no electret material 48, there is no charge. Attaching the conductive layer 34 of the master sheet to ground, e.g. by connection to the drum 54, precludes random triboelectric charging in background areas. It will also be appreciated that powdered toner can be used with equal facility in place of liquid toner.

In the embodiment illustrated in FIGS. 13, the transfer material utilized is carnauba wax and is ideally suited for thermal transfer and electret formation. However, the foregoing process is generally useful with any electret material, particularly material which can be thermally transferred or transferred under the impact conditions to be described hereinafter. The term "electret" is used in its generally accepted sense to define a permanently electrified substance which under ordinary conditions has electrical charges of opposite sign at opposite major surfaces. Useful electret layers for recording can be characterized further as volume polarized" so that a number of subsurface charges of the same sign adjacent one major surface are opposite an approximately equal number of subsurface charges bearing the opposite sign located adjacent the opposite major surface. A suitable electret charge distribution is readily obtained with polar dielectric materials whose molecules are permitted to move in an electric field whereupon the positively charged ends of the molecules become aligned adjacent one major surface while the negatively charged ends become aligned adjacent the opposite major surface.

Electret materials which are particularly suitable for thermal transfer are heat softenable dielectric substances which possess a finite dipole moment in the liquid or softened state. Examples of such materials include: such natural organic products as carnauba wax and carnauba wax-bees wax mixtures; mixtures of wax such as carnauba wax with various synthetic thermoplastic polar resins such as polyvinyl chloride; and polar plastic materials themselves including selected vinyls, acetals, acrylics, polyesters and silicones. Other electret materials are known to the art and reference can be made to the patents to Gaynor, Polke, Schwertz, Padgett, Fehlberg et a1. and Gunning et al., as described above.

In the embodiment depicted in FIGS. 1-3, the components are arranged so that the original document 14 is exposed to infrared radiation through both the receiving sheet 18 and transfer sheet 16 whereby the transfer material 24 is transferred in mirror image fashion enabling the master sheet 18 to be used to produce right-reading copies. Accordingly, both the master sheet 18 and transfer sheet 16 should be transparent to infrared radiation. However, other methods for arranging the components can be utilized. For example, the base sheet 12 can be omitted, or the base sheet 12 can be transparent to infrared radiations, and radiation conducted through the original document 14.

In order to impose a potential gradient across the transfer material, it is desirable that both the transfer sheet 16 and master sheet 18 be electrically conductive. In the configuration shown, it is desirable that both the transfer sheet 16 and master sheet 18 be sub stantially more transparent to infrared radiation than is conductive paper, and accordingly it is convenient to utilize the Mylar sheet as above described provided with a thin layer of transparent electrically conductive material. A thin transparent conducting metal film can be deposited on the surface of the Mylar base film by well known vacuum deposition techniques. Transparent conducting film exhibiting a variety of electrical characteristics are known and may be prepared from chromium, iron, nickel, as well as such metallic compounds as indium oxide and cuprous iodide. A detailed description of a method and apparatus for producing such a cuprous iodide film is disclosed in US Pat. No. 2,756,l65 entitled Electrically Conducting Films and Processes Forming Same" by D. A. Lyon. A thin surface film of the solid electret-forming composition may be deposited on the conducting layer by conventional techniques such as coating the surface with an organic liquid solution of the electret-forming material and thereafter evaporating the solvent.

The image-receiving surface of the master sheet 18 preferably has greater affinity for the electret or electret-forming material, either in a softened state or in an impact state as hereinafter described, so that such material can be readily transferred to the master sheet. Such preferential affinity can be accomplished by utilizing as a conductive layer on the master sheet 18 a metal layer which has greater affinity for the electret or electret-forming material than does the conducting layer deposited on the transfer sheet. Alternatively, the conducting master sheet layer 30 can be textured so as to provide a multiplicity of contact points for the transfer material, thereby resulting in preferred affinity for the material. Alternatively, the master sheet can be formed of material which does not require a thin metallic coating or the like, particularly where transparency to infrared radiation is not important. In such case, the receiving surface can be made as receptive as desirable for the transfer material by appropriate physical or chemical modification as is well known to the art.

Referring now to FIGS. 4a and 4b, an alternative embodiment is illustrated in which the components are similar in construction and arrangement to the components depicted in FIGS. 1-3, but in which the transfer material is preformed as electret. In accordance with this embodiment, a transfer sheet 82 is formed with a thin conductive layer 84 on which is coated a layer 86 of electret material. The electret material layer 86 can be formed of carnauba wax and be chemically identical to the transfer material 24 referred to hereinbefore except that the entire layer is pre-converted to electret form. This can be accomplished by merely heating the entire layer in the presence of a polarizing potential and reference can be made to the aforementioned patents, for example, Gaynor Pat. No. 3,276,03]. A receiving sheet 88 which may be identical to the receiving sheet 18 of FIGS. 1-3, formed with a thin electrically conducting layer defining its receiving surface, is pressed into contact with the electret layer 86. The sandwiched assembly is placed on an original document 92 containing indicia 94 to be duplicated and supported on a base sheet 96.

A DC potential gradient from a voltage source 98 is placed across the electret material 86 by contact with the electrical conductive layers 84 and 90, in a manner similar to that depicted in FIG. 2a. The polarity of the potential gradient is preferably arranged to be in the same direction as the polarity of the electret layer. While under this potential gradient, the assembly is subjected to infrared radiation, as indicated at 100 so as to penetrate the receiving sheet 88 and transfer sheet 82 and impinging onto the original document 92, generating a temperature rise in the image portions 94 of the document 92 resulting in a thermal pattern emanat' ing from the document 92. As a result of the generation of a thermal pattern, the electret material 86 is selectively fused to a softened condition in regions corresponding to the indicia 94. The fused, softened electret material 102 is transferred to the receiving sheet surface 90 to produce an image 90 which corresponds to the image defined by the indicia 94 on the original document 92.

Referring particularly to FIG. 4b, after the infrared radiation exposure has been terminated, and the sandwiched assembly cooled, the receiving sheet 88 may be moved from the assembly and will carry the fused regions 102 of the transfer material layer 86 away from the transfer sheet 82. The process steps are identical to the process steps described with respect to FIGS. 1, 2a and 2b; however, as a result of utilizing the preformed electret material as the transfer material layer 86, both the receiving sheet 88 and transfer sheet 82 can carry an image pattern defined by electret material. The receiving sheet 88 carries the electret material in the form of a positive image in direct correspondence to the indicia 94 of the original document 92. On the other hand, the transfer sheet 82 carries electret material in the form of a negative image in inverse correspondence to the indicia 94 of the original document 92. One can utilize either the receiving sheet 88 or transfer sheet 82 as a master for subsequent duplication to obtain positive or negative copies, respectively.

Referring to FIG. 5, another embodiment is illustrated wherein electret material is transferred by impact. A transfer sheet 104 is provided which is similar to the transfer sheet of FIGS. 40 and 4b, having a thin layer 106 of electrically conductive material on one surface and coated thereon a layer 108 of pre-formed electret-material. A receiving sheet 110 having its receiving surface defined by a thin layer 112 of electrically conductive material is disposed with its receiving layer I12 in contact with the electret layer 108. While in such position, information to be recorded is typed onto the rear of the transfer sheet so as to result in a plurality of depressions 114 into the transfer sheet and to transfer impacted regions 116 to the receiving sheet I10. Upon separation of the receiving sheet 110 from the transfer sheet 104, the impacted electret regions 116 are carried away from the transfer sheet I04. Either the receiving sheet 110 or the transfer sheet 104 can then be utilized as master sheets to produce positive or negative copies, respectively.

In the embodiment of FIG. 5, it is not necessary that either the transfer sheet 104 or receiving sheet I10 be transparent. Accordingly, the substrates of these components can be formed of paper, or any other conventional material. Although the sandwiched assembly is not subjected to a polarizing potential during formation or transfer of the image, the electrically conductive layers 106 and 112 act as keepers for the electret material, allowing greater shelf life. Additionally, if the transfer sheet 104 is to be utilized as a master sheet, for obtaining negative copies of the impact-transferred information, then provision of a conductive layer such as 106 is desirable for subsequent electrostatic transfer of toner in accordance with the process of FIG. 3. On the other hand, if the transfer sheet is to be merely dis carded, and long shelf life is not a critical factor, then a simple paper transfer sheet substrate can be utilized.

Referring to FIGS. 6a, 6b and 60, there is illustrated still another embodiment of the present invention for impact transfer of electret-forming material. A transfer sheet 1 18 of paper, or other inexpensive substrate material, is coated with a layer 120 of electret-forming material, such as carnauba wax. A receiving, master sheet 122 is formed of paper backing 124 with a thin layer 126 of electrically conductive material defining a receiving surface. The master sheet 122 is positioned with its receiving surface 126 in contact with the electret-forming layer 120 and information to be duplicated is typed onto the back of the transfer sheet 118, as indicated by the depressions I28. Impacted electretforming material 130 is thus transferred to the transfer sheet 122 which, when peeled from the assembly as shown in FIG. 6a, carries the impacted electret-forming material I30 away from the transfer sheet 118. There is formed a master sheet 122 carrying an image to be duplicated in the form of impacted electret-forming material 130 raised in relief from the surface 126 of the master sheet 122.

Referring particularly to FIG. 6b, a heating electrode plate 132 is placed in contact with the impacted electret-forming material 130 and a voltage source 134 is connected to the plate 132 and to the electrically conducting receiving sheet layer 126. A D-C gradient is placed across the impacted material while the impacted material is heated to its softening temperature by the plate 132 so that the impacted material 130 is polarized to electret form. Referring particularly to FIG. 6c, a master sheet 122 is provided with an image of the information to be recorded in the form of electret material 130 raised from its surface 126. The master sheet 122 can be placed on the drum 54 of the apparatus depicted in FIG. 3 and utilized to produce a plurality of copies in accordance with that process.

I claim:

I. In an electrostatic copy process, the steps of:

providing a transfer sheet having a surface coated with electret-forming, heat softenable, solid transfer material;

positioning a receiving sheet for said transfer material in contact with said transfer material; applying a D-C potential across said transfer material;

therrnally forming a design on said transfer material in the form of heat-softened transfer material for 9 transfer of said softened transfer material to said receiving sheet; cooling said transfer material to solid form while said D-C potential is applied; and separating said receiving sheet from said transfer sheet whereby to carry said design on the surface of said receiving sheet in the form of a charged design of electret material raised in relief from said surface;

applying toner to said charged design of raised, electret material; positioning a copy sheet in surface contact with the toned side of said raised electret material; transferring toner from said raised electret material to said copy sheet to form said design in the form of toner thereon; and separating said copy sheet from said receiving sheet. 2. The invention according to claim 1 in which said electret material comprises carnauba wax.

3. In an electrostatic copy process, the steps of: providing a transfer sheet having a surface coated with heat softenable, solid electret material; positioning a receiving sheet for said electret material in contact with said electret material;

applying a D-C potential across said electret material without destroying the electret properties thereof;

heat-softening said electret material in selected areas to constitute a design and to transfer said softened electret material to said receiving sheet;

cooling said softened electret material to solid form while said D-C potential is applied; and

separating said receiving sheet from said transfer sheet whereby to carry said design on the surface of said receiving sheet in the form of a charged design of electret material raised in relief from said surface;

applying toner to said charged design of raised, electret material;

positioning a copy sheet in surface contact with the toned side of said raised electret material;

transferring toner from said raised electret material to said copy sheet to form said design in the form of toner thereon; and

separating said copy sheet from said receiving sheet.

4. The invention according to claim 3 in which said electret material comprises carnauba wax, 

1. In an electrostatic copy process, the steps of: providing a transfer sheet having a surface coated with electret-forming, heat softenable, solid transfer material; positioning a receiving sheet for said transfer material in contact with said transfer material; applying a D-C potential across said transfer material; thermally forming a design on said transfer material in the form of heat-softened transfer material for transfer of said softened transfer material to said receiving sheet; cooling said transfer material to solid form while said D-C potential is applied; and separating said receiving sheet from said transfer sheet whereby to carry said design on the surface of said receiving sheet in the form of a charged design of electret material raised in relief from said surface; applying toner to said charged design of raised, electret material; positioning a copy sheet in surface contact with the toned side of said raised electret material; transferring toner from said raised electret material to said copy sheet to form said design in the form of toner thereon; and separating said copy sheet from said receiving sheet.
 2. The invention according to claim 1 in which said electret material comprises carnauba wax.
 3. In an electrostatic copy process, the steps of: providing a transfer sheet having a surface coated with heat softenable, solid electret material; positioning a receiving sheet for said electret material in contact with said electret material; applying a D-C potential across said electret material without destroying the electret properties thereof; heat-softening said electret material in selected areas to constitute a design and to transfer said softened electret material to said receiving sheet; cooling said softened electret material to solid form while said D-C potential is applied; and separating said receiving sheet from said transfer sheet whereby to carry said design on the surface of said receiving sheet in the form of a charged design of electret material raised in relief from said surface; applying toner to said charged design of raised, electret material; positioning a copy sheet in surface contact with the toned side of said raised electret material; transferring toner from said raised electret material to said copy sheet to form said design in the form of toner thereon; and separating said copy sheet from said receiving sheet.
 4. The invention according to claim 3 in which said electret material comprises carnauba wax. 